How is a balance between a host and a parasite
achieved? What is heard immunity, how is it achieved and how does it protect a
population? Does everyone have to be immunized to achieve herd immunity? Why?

- As the host population develops resistance, the spread of the

pathogen is checked, and eventually a balance is reached in which host and

pathogen are in equilibrium.

- Herd immunity is the resistance of a group to infection due to

immunity of a high proportion of the members of the group.If a high proportion

of individual sin a group are immune to an infectious agent, then the whole

population will be protected.

- No, if a population is 70% immunized it will be absent from the population, the immunized individuals protect the rest of the population because they cannot acquire and pass on the pathogen, thus breaking the cycle of infection.

Where are the most cases of AIDS found and how
are most cases of HIV transmitted?

- The most cases of AIDS is found in Sub-Saharan Africa.

- Transmitted during sexual activity or by blood-contaminated needles.

What
are the three most common types of nosocomial infections and what organisms are
most often associated with each?

• Staphylococcus spp., particularly S. aureus., cause wound and

blood infections, pneumonia.

• Escherichia

coli , Enterococcus spp., Pseudomonas

aeruginosa, Candida albicans, Klebsiella pneumonia - urinary

infections.

• Staphylococcus spp., Enterococcus spp. and Escherichia coli

have tendency to have multiple drug resistance

. What are the major factors leading to a spread
of nosocomial infections? Why are hospital patients more susceptible than
normal individuals to pathogens?

Major factors leas=ding to a spread of nosocomial infections:

-

Many patients have low resistance to infectious disease because of

their illness

- Healthcare facilities treat infectious disease patients, and these

patients may be pathogen reservoirs

- Multiple patients in rooms and wards increace the chance of cross-infection

- Healthcare personnel move from patient to patient, increasing the probability of transfer of pathogens

- Healthcare procedures such as hypodermic injection, spinal puncture, and removal of tissue samples or fluids, breach the skin barrier and may introduce pathogens into the patient

- In maternity wards of hospitals, newborn infants are unusually susceptible to certain infections because they lack well-developed defense mechanisms

- Surgical procedures expose internal organs to sources of contamination, and the sress of surgery often diminishes the resistance of the

patient to infection

- Certain therapeutic drugs, such as steroids used for controlling inflammation, increase the susceptibility to infection

- Use of antibiotics to control infections selects for

antibiotic-resistant organisms.

What are the common public measures used for
controlling of an infectious disease? Compare public measures for controlling
infectious disease caused by insect reservoirs and by human carriers.

rubella, polio. Hepatitis A and B. Bacterial pneumonia and meningitis.

What public health methods can be used to halt
the spread of an epidemic disease once it has begun?

• Quarantine -

– time limit for quarantine is the longest period of the

communicability of the given disease

– Cholera, plague, yellow fever, relapsing fever, typhoid fever,

smallpox. Ebola hemorrhagic fever and meningitis is some cases.

• Surveillance, reportable diseases in Table 33.5

• Pathogen Eradication

– Small pox in 1980.

– Polio, leprosy, Chagas’ disease, dracunculiasis are targeted as of

now.

– Candidates syphilis and rabies.

Contrast mortality due to infectious diseases in
Africa and the Americas.

Causes of death in the Americas and Africa, 2002. (a) Africa; (b) the Americas. There were 10.7 million deaths in Africa, 6.7 million due to infectious diseases. There were 6 million deaths in the Americas, 623,000 due

to infectious diseases.

What are some examples of recent outbreaks of
emerging or re-emerging infectious diseases? What are the factors leading to
emergence and reemergence of infectious diseases? What emerging and reemerging
diseases are most important?

1. Human demographics.

– Cities versus country living.

– Sexual and other risk behavior.

2. Technology and industry.

– General improvement in public health

– Nocosomial diseases

– Transportation, central distribution

3. Economic development and

land use.

–

Lyme disease in the US

– Rift Valley disease in Egypt.

4. International travel and

commerce.

– West Nile virus, Marburg (Ebola) virus

5. Microbial adaptation and

change.

– RNA viruses: SARS, influenza and HIV virus.

6. Breakdown of public

health measures.

– Cryptosporidium outbreak in Wisconsin

– Diphtheria in the Soviet Union

7. Abnormal natural

occurrences that upset the usual host-pathogen balance.

– Hantavirus and mice

How are the problems of emerging and
re-emerging diseases addressed by public health officials?